Magnetic particle inspection apparatus wherein the accumulated particles close the indicator circuit

ABSTRACT

An automatic magnetic particle inspection apparatus for detecting a defect in the workpiece and for signalling the presence of the defect in the workpiece is disclosed. The apparatus has conveying means for supporting the workpiece, drive means connected to one of the conveying means and the apparatus for causing relative movement between the conveying means and the apparatus to convey the workpiece along a path of movement; magnetizing means disposed adjacent a path of movement of the workpiece and for creating lines of flux in the workpiece and fringe lines of flux adjacent the defect in an attraction zone; magnetic particles spray means disposed further along the path of movement of the workpiece for spraying magnetic particles on the magnetized workpiece to deposit the particles on the workpiece in a spray zone adjacent the attraction zone and to create a pile of the magnetic particles adjacent the defect in the attraction zone within the spray zone; and detecting and signalling means disposed further along the path of movement of the workpiece. The detecting and signalling means has a bi-pole detecting head which is spaced from the attraction zone a predetermined distance and has magnet means and a contact member for contacting the workpiece. The magnet means is operable to create lines of flux through one pole of the detecting head, the contact member, the workpiece, the pile of magnetic particles, the other pole of the detecting head to the magnet means to form the pile of magnetic particles and into a bridge across the predetermined distance. Signal means are employed for indicating the presence of the defect and control means are connected to the detecting head and the signal means and are energized by the bridge to actuate the signal means to indicate the presence of the defect.

United States Patent Zemberry [54] MAGNETIC PARTICLE INSPECTION APPARATUS WHEREIN THE ACCUMULATED PARTICLES CLOSE THE INDICATOR CIRCUIT William L. Zemberry, Swissvale Borough, Pa.

United States Steel Corporation July 30, 1970 [72] Inventor:

[73] Assignee:

[22] Filed:

21 Appl. No.: 59,407

Primary Examiner-Rudolph V. Rolinec Assistant Examiner-R. J. Corcoran Attomey-Robert J. Leek, Jr.

[57] ABSTRACT An automatic magnetic particle inspection apparatus for de- [451 June 6,1972

tecting a defect in the workpiece and for signalling the presence of the defect in the workpiece is disclosed. The apparatus has conveying means for supporting the workpiece, drive means connected to one of the conveying means and the apparatus for causing relative movement between the conveying means and the apparatus to convey the workpiece along a path of movement; magnetizing means disposed adjacent a path of movement of the workpiece and for creating lines of flux in the workpiece and fringe lines of flux adjacent the defeet in an attraction zone; magnetic particles spray means disposed further along the path of movement of the workpiece for spraying magnetic particles on the magnetized workpiece to deposit the particles on the workpiece in a spray zone adjacent the attraction zone and to create a pile of the magnetic particles adjacent the defect in the attraction zone within the spray zone; and detecting and signalling means disposed further along the path of movement of the workpiece. The detecting and signalling means has a bi-pole detecting head which is spaced from the attraction zone a predetermined distance and has magnet means and a contact member for contacting the workpiece. The magnet means is operable to create lines of flux through one pole of the detecting head, the contact member, the workpiece, the pile of magnetic particles, the other pole of the detecting head to the magnet means to form the pile of magnetic particles and into a bridge across the predetermined distance. Signal means are employed for indicating the presence of the defect and control means are connected to the detecting head and the signal means and are energized by the bridge to actuate the signal means to indicate the presence of the defect.

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SHEET 70F 7 14 98/4 X1 1 '5 ,1 3 I t:- Movement of I ij/ /2 1 4 L I 56 l Line of Contact I z/ of Bridged Far- I /7 I ,I IV 4\ O D. 6. Supply INVEN TOR. WILLIAM L. ZEMBERRY A Horney MAGNETIC PARTICLE INSPECTION APPARATUS WHEREIN THE ACCUMULATED PARTICLES CLOSE THE INDICATOR CIRCUIT BACKGROUND OF THE INVENTION Heretofore in the area of non-destructive inspection of magnetizable workpieces, such as pipes, bars, billets, plates or the like, for defects or discontinuities, such as cracks, roll marks, score lines, non-metallic foreign bodies and the like, ultrasonic methods, eddy current methods, fluorescent particle methods, magnetic particle methods and the like have been employed. Of these methods, the magnetic particle inspection system or method is probably the most effective system for indicating such surface defects or discontinuities and is acceptable under most inspection specifications. This system is practical because of its low initial cost, the ruggedness of the equipment and the small amount of maintenance required by mill or plant personnel. However, the potential of the magnetic particle inspection system has never been fully realized because of its dependence on the diligence of the human inspector who observes the buildup of the adhesive particles at the defects or discontinuities of the workpiece and marks the location of defects or discontinuities on the workpiece.

OBJECTS OF THE INVENTION It is the general object of this invention to avoid and overcome the foregoing and other difficulties of and objections to prior art practices by the provision of an improved magnetic particle inspection apparatus, which:

a. is rugged in construction thereby enabling the apparatus to withstand severe mill or plant operating conditions;

b. requires little or no maintenance;

c. operates on a magnetic bridging or switching principle thereby permitting the use of semi-skilled or unskilled operators;

d. has a low installation cost;

e. utilizes a non-contact sensing feature which eliminates wear on the apparatus;

f. provides a maximum utilization of magnetic power through positive contact of one pole of the apparatus with the workpiece; and

g. provides a simple method of automating such apparatus.

BRIEF SUMMARY OF THE INVENTION The aforesaid objects of this invention and other objects which will become apparent as the description proceeds are achieved by providing an automatic magnetic particle inspection apparatus for detecting a defect in a workpiece and for signalling the presence of the defects in the workpiece. The apparatus has conveying means for supporting the workpiece, drive means connected to one of the conveying means and the apparatus for causing relative movement between the conveying means and the apparatus to convey the workpiece along a path of movement; magnetizing means disposed adjacent a path of movement of the workpiece and for creating lines of flux in the workpiece and fringe lines of flux adjacent the defeet in the attraction zone; magnetic particles spray means disposed further along the path of movement of the workpiece for spraying magnetic particles on the magnetized workpiece to deposit the particles on the workpiece in a spray zone adjacent the attraction zone and to create a pile of the magnetic particles adjacent the defect in the attraction zone within the spray zone; and detecting and signalling means disposed further along the path of movement of the workpiece. The detecting and signalling means has a bi-pole detecting head which is spaced from the attraction zone a predetermined distance and has magnet means and a contact member for contacting the workpiece. The magnet means is operable to create lines of flux through one pole of the detecting head, the contact member, the workpiece, the pile of magnetic particles, the other pole of the detecting head to the magnet means to form the pile of magnetic particles into a bridge across the predetermined distance. Signal means are employed for indicating the presence of the defect and control means are connected to the detecting head and the signal means, and are utilized by the bridge to actuate the signal means to indicate the presence of the defect.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS For a better understanding of this invention, reference should be had to the accompanying drawings wherein like numerals of reference indicate similar pans through the several views and wherein:

FIG. 1 is a diagrammatic side elevational view of the automatic magnetic particle inspection apparatus of the present invention and showing the workpiece, in this case a hollow pipe supported on the conveying means, the magnetizing means, the magnetic particle spray means, the particle collecting means, and the automatic detecting and marking means and also showing the drive means connected to the conveying means;

FIG. 1A is a diagrammatic end elevational view taken along the lines IA1A of FIG. 1 in the direction of the arrows and showing the details of the magnetizing means;

FIG. 1B is a diagrammatic end elevational view of the pipe showing the magnetic lines of flux induced in the pipe and the fringe flux lines disposed about the defect in the pipe and the which defect, in this case, is a partial crack or a discontinuity therein;

FIG. 1C is an enlarged fragmentary side elevational diagrammatic view showing the lines of fringe flux and lines of flux in the pipe of FIG. 13;

FIG. 2 is a diagrammatic side elevational view taken along the lines 2-2 of FIG. 1 in the direction of the arrows and showing the details of the magnetic particle spraying means;

FIG. 3 is a view similar to FIG. IC with the lines of flux and fringe flux omitted therefrom and showing a magnetic particle buildup in and around the defect in the attraction zone and further showing the spray zone in which the magnetic particles are deposited by the magnetic particle spray means and the particle buildup zones adjacent the attraction particle attraction zone wherein the magnetic particles are piled on the workpiece;

FIG. 4 is a diagrammatic side elevational view of the particle collecting means taken along the line 44 of FIG. 1 in the direction of the arrows;

FIG. 5 is a diagrammatic side elevational view of the detecting and signalling means taken along the line 55 of FIG. 1 in the direction of the arrows;

FIG. 6 is an enlarged fragmentary cross-sectional and diagrammatic view of the detecting head and contact means of the detecting and signalling means;

FIG. 7 is a diagrammatic fragmentary side elevational view of the contact means of the detecting and signalling means taken along the line 77 of FIG. 6 in the direction of the arrows;

FIG. 8 is a fragmentary side elevational view similar to FIG. 6 of an alternative embodiment of the detecting head and magnet means for use with a flat plate or bar;

FIG. 9 is a view similar to FIG. 1 showing the drive means connected to the apparatus;

FIG. 10 is an end elevational view of the apparatus shown in FIG. 9;

FIG. 1 l is a wiring diagram of an alternative embodiment of the control means;

FIG. 12 is a side elevational view of an alternative embodiment having two detecting heads to provide complete peripheral detection of the workpiece;

FIG. 13 is a vertical sectional view taken along the line 13- 13 of FIG. 12 in the direction of the arrows; and

FIG. 14 is a schematic perspective view of another alternative embodiment showing only one set of rolls including a concave roll type detection head and a concave roll type contact roll to accommodate a wide range of sizes of workpieces.

DETAILED DESCRIPTION With specific reference to the form of this invention illustrated in the drawings and referring particularly to FIG. 1, an automatic magnetic particle inspection apparatus for detecting a defect, such as a partial crack (FIGS. lA-lC) or the like, in a workpiece, such as a pipe 12 (FIGS. 1, 1A-1C, 2, 3, 4, 5, 6, 9, 10) or the like, and for signalling the presence of the defect 10 in the workpiece 12 is indicated by the reference numeral 14. The apparatus 14 has conveying means 16 (FIGS. 1, 2, 9, 10) for supporting the workpiece l2.

CONVEYING MEANS 16 The conveying means 16 comprises a plurality of conveyor stands 18 (FIGS. 1, 2, 9, 10) in which are joumaled supporting rollers 20 (FIGS. 1, 1A, 2, S, 9, 10) on which the workpiece or pipe 12 is supported.

Drive means (FIGS. 1, 9, 10) are connected to one of the conveying means 16 and the apparatus 14 for causing relative movement between the conveying means 16 and the apparatus 14 to convey the workpiece 12 along a path of movement indicated by the arrows in FIG. 1. In FIG. 1, the drive means comprises a motor 22 connected to one or more of the rollers 20.

Magnetizing means 24 (FIGS. 1, 1A) are disposed adjacent the path of movement of the workpiece 12 and are'utilized to create lines of flux 26 (FIGS. lA-IC) in the workpiece or pipe 12 and also fringe lines of flux 28 (FIGS. 18, 1C) adjacent the crack 10in an attraction zone 2,, (FIG. 3).

MAGNETIZING MEANS 24 As shown in FIGS. 1 and 1A, the magnetizing means 24 has a V-shaped frame 30 upstanding from a bedplate 32 (FIGS. 1, 1A). For the purpose of positioning a pair of magnetizing coils 34 (FIGS. 1, 1A) with respect to the pipe or workpiece 12, such coils 34 are mounted on slides 36a, 36b (FIG. IA) which slides 36a, 36!: are reciprocable in the upper surface of each arm 38 of the V-shaped frame 30. The means utilized to position the right-hand slide 36a comprises a threaded nut 40 carried by the slide 360, which threaded nut 40 (FIG. 1A) is rotatable on and movable by a screw 42a (FIG. 1A). The screw 42a is joumaled in bearings 44 (FIG. 1A) and is rotatable by the handle 46a (FIG. 1A). The left-hand slide 36b (FIG. 1A) carries a rack 48 (FIG. 1A) which rack '48 is engageable by a pinion 42b similarly joumaled in bearings 44 and rotatable by a handle 46b. The magnetizing coils 34 are connected by lines L L (FIG. 1A) to a suitable source of DC supply, indicated by the legend DC supply. As shown in FIG. 1A, the slides 36a, 36b carry pole pieces 50a and 50b respectively which are surrounded by the magnetizing coils 34 and are positionable by movement of the slides 36a, 36!; with respect to the pipe 12 carried by the supporting rollers 20.

As shown in FIG. 1, magnetic particle spray means 52 (FIGS. 1,2) are disposed further along the path of movement of the workpiece 12 (to the right as shown in FIG. 1) for spraying magnetic particles 54 (FIGS. 1, 3, 6) on the now magnetized pipe 12 to deposit the magnetic particles 54 (FIG. I, 2, 3) on the pipe 12 in a spray zone Z, (FIG. 3) adjacent the attraction zone Z and to create a pile 56 (FIG. 3) of magnetic particles 54 adjacent the crack 10 in the attraction zone 2,, within the spray zone 2,. The magnetic particle spray means 52 deposits or lays, as shown in FIG. 3, the magnetic particles 54 on the surface of the pipe 12 in a particle buildup zone Z (FIG. 3) on either side of the attraction zone Z, and within the spray zone Z,.

MAGNETIC PARTICLE SPRAY MEANS 52 As shown in FIGS. 1, 2, 3, the magnetic particle spray means 52 has a frame 58 (FIGS. 1, 2) upstanding from bed plates 60 (FIGS. 1, 2) for the purpose of providing a spray of magnetic particles 54 to the magnetized pipe 12. A hopper 62 (FIGS. 1, 2) depends from the upper arm 64 (FIGS. 1, 2) of the frame 58 and magnetic particles 54 are fed (and aided in the feeding by a vibrator 66 (FIGS. 1, 2) mounted on the side wall of the hopper 62) by means of a T" connection 68 (FIGS. 1, 2) into a spray line 70 (FIG. 1). This spray line 70 extends from a source of compressed fluid, such as compressed air or the like, indicated by the legend from air supply", to a spray nozzle or sprayer 72 (FIGS. 1, 2). This sprayer 72 deposits the magnetic particles 54 in the spray zone Z, shown in FIG. 3.

As shown in FIGS. 1, 4, the apparatus 14 has a magnetic particle collecting means 74 (FIGS. 1 and 4) disposed further along the path of movement of the workpiece 12 (FIG. 1) to collect the magnetic particles 54 lying within the particle buildup zone Zp (FIG. 3) in the spray zone Z MAGNETIC PARTICLE COLLECTING MEANS 74 The magnetic particle collecting means 74 has a frame 76 (FIGS. 1, 4). In order to remove the loosely held magnetic particles 54 in the particle buildup zone Z (FIG. 3) from the pipe 12, a line 78 (FIGS. 1, 4) extends from a compressed fluid supply, such as a compressed air supply or the like, indicated by the legend from air supply (FIG. 4) to a nozzle 80 (FIGS. 1, 4). This nozzle 80 blows the loosely held magnetic particles 54 in the particle buildup zone 2;. (FIG. 3) into afunnel 82 (FIGS. 1, 4) disposed diametrically opposite to the noule 80. The line 78 and funnel 82 are supported by chains 79 (FIGS. 1, 2) depending from an upper arm 81 of the frame 76. For the purpose of providing a suction means to collect the magnetic particles 54in the funnel 82 and transport them via a collecting tube 84 (FIGS. 1, 4) in the direction of the arrows (FIG. 4), the tube 84 is connected to a fan 86 (FIGS. 1, 4) driven by a motor 88 (FIG. 4) and thence from the bottom of the fan 86 into the top of a cyclone type dust collector 90 (FIGS. 1, 4). The cyclone type dust collector 90 is of the type SDC manufactured by Ducon Co., Inc., Mineola, New York and provided with separating baffles 92 (FIG. 4). When the compressed air and the entrained magnetic particles 54 enter the dust collector 90, the fluid and magnetic particles 54 encounter a plurality of these separating bafiles 92 (FIG. 4) where the magnetic particles 54 are passed to the bottom of the dust collector 90 and are collected adjacent a discharge gate 94 (FIG. 4). The compressed air or fluid exits from the dust collector via a vent 96 (FIGS. 1, 4) at the top of the dust collector 90.

Detecting and signalling means 98 (FIGS. 1, 5, 6 and 7) are disposed further along the path of movement of the workpiece ofpipe 12 (FIG. 1).

DETECTING AND SIGNALLING MEANS 98 The detecting and signalling means 98 has an adjustable frame 100 (FIGS. 1, 5) upstanding from the floor of ground adjacent the apparatus 14. In addition, the detecting and signalling means 98 has a detecting device provided with a detecting head 102 (FIGS. 1, 5, 6) mounted on a shaft 104 (FIGS. 1, 5, 6, 7) joumaled in a drum support 106 (FIGS. 1, 5) secured to an upper arm 108 (FIGS. 1,5) of the frame 100 as by bolts 109 (FIG. 5) or the like and insulated from the upper arm 108 by means of an insulating plate 110 (FIGS. 1, 5) suitably Micarta or the like. Micarta" is a trade name of the Westinghouse Electric Corporation, Pittsburgh, Pennsylvania, for a laminated sheet. In order to rotate the detecting head 102 in the direction of the arrows shown in FIGS. 1, S and 6, a head drive means 112 (FIGS. 1, 5) is provided.

HEAD DRIVE MEAN 1 12 As shown in FIGS. 1 and 5, the head drive means 112 has a drive pulley 114 (FIG. I) on a shaft 115 joumaled in brackets 117 (FIG. I) in engagement and driven by the pipe 12. The pulley 114 is connected by a belt 116 (FIGS. 1, 5) to the driven pulley 118 on the shaft 104.

For the purpose of tensioning the belt 116, a tensioning device 120 (FIGS. 1,5) is mounted on the side of the drum support 106 and is secured in the desired tensioning position by means of a bolt 122 (FIGS. 1, 5) or the like. The tensioning device 120 has an arm 124 (FIGS. 1, 5) which carries a tensioning pulley 126 (FIGS. 1, 5) on a stud shaft 128 (FIGS. 1, 5) projecting from the lower end of the arm 124 and riding in tensioning engagement with a belt 1 16.

As shown particularly in FIG. 6, the bi-pole detecting head 102 is fonned into a south pole portion S and north pole portion N and formed of a magnetizable material, such as mild steel or the like. The south pole S is separated from the north pole N by means of an insulating disk 132 (FIG. 6), suitably formed of Micarta or the like and the south pole S is held to the north pole N by means of an insulating bolt 130 (FIG. 6) or the like, suitably formed of nylon or the like. Disposed within a magnetic cavity 134 (FIG. 6) within the detecting head 102 is a magnetic means, suitably a permanent magnet 136 (FIG. 6) or the like formed of Alnico or the like. Alnico is a trade name of the General Magnetic Corporation, Detroit, Michigan for the permanent magnet 136 (FIG. 6) which magnet 136 is insulated from the shaft 104 by means of an insulating bushing 138 (FIG. 6) formed of Micarta or the like, and has a south pole S (FIG. 6) and a north pole N (FIG. 6). As shown in FIG. 6, the detecting head 102 is spaced from the attraction zone 2,; of pipe 12 a predetermined distance d (FIG. 6). In addition, the detecting head 102. has a contact member, suitably a contact disk 140 (FIG. 6) or the like, which floats by means of a clearance cavity 142 (FIG. 6) in vertical reciprocating movement on the shaft 104 and (being of magnetizable material such as mild steel or the like) is secured to the right-hand portion or side face of the detecting head 102 by magnetic force. In normal operation, the contact disk 140, due to its weight and magnetic attraction to pipe 12, slides downwardly into en- EagYTeTwRITthe pipe or workpiece 12 as shown in- FIG. 6. The zone of inspection Z, (FIG. 6) extends from the left-hand lower edge of the detecting head 102 to the left- OPERATION OF'MAGNET 136 The permanent magnet 136 is operable to create lines of flux 142' from, for example, the north pole N of the permanent magnet 136 through one pole, such as the north pole N of the detecting head 102, the contact disk 140, the pipe 12, the pile 56 of magnetic particles 54 adjacent the crack 10, the other pole S of the detecting head 102 to the other pole S of the permanent magnet 136 to magnetize the pile 56 (FIG. 3) of magnetic particles 54 into a bridge 56 (FIG. 6) across the predetermined distance (1.

Control means 144 (FIGS. 1, 6) are connected to the detecting head 102 and to a signal means 146 (FIG. 1) for in dicating the presence of the defect in the pipe 12) and are energized by the bridge 56 (FIG. 6) to activate the signal means 146 to indicate the presence of the defect or crack 10.

CONTROL MEANS 144 The control means 144 (FIGS. 1, 6 and 7) has a contact assembly 148 (FIGS. 5, 6, 7) associated with the shaft 104. This contact assembly 148 has a conducting ring 150(FIGS. 6, 7) suitably of bronze or the like mounted by means of a bolt 152 (FIG. 6) on the shaft 104. In addition, the control means 144 has a brush contactor 154 (FIGS. 6, 7) mounted by means of an insulating plate 156 (FIGS. 5, 6, 7) on the frame 100 in contact with the rotating conducting ring 150, which brush contact 154 is connected by a line 1., (FIGS. 1, 6, 7) to a control device such as, for example, an amplifier 158 (FIG. 1) of the sensitive solid state metering relay of the Model 12 type manufactured by Sensitak Instrument Corporation, Manchester, New Hampshire.

As shown in FIG. 1, the amplifier 158 is mounted on the arm 108 of the frame and is connected by lines L and L, (FIG. 1) to a suitable source of electrical supply indicated by the legend AC or DC supply.

SIGNAL MEANS 146 As mentioned above generally, the amplifier 158 is connected by a line L (FIG. 1) to a signal means, such as a visible signal means 160, such as an incandescent light or the like. Another line L, (FIG. 1) connects both the incandescent light 160 and the amplifier 158 to the ground.

OPERATION OF CONTROL MEANS 144 Referring particularly to FIG. 6, it will be understood by those skilled in the art that after the formation of the bridge 56 of the magnetic particles 54 adjacent the crack 10 a current flows in the direction of the dotted arrows 142 shown in FIG. 6 from the amplifier 158 through the contact assembly 148, shaft 104, detecting head 102, bridge 56, pipe 12 and through a ground connection L (FIG. 6) to ground. This signal current is amplified by the amplifier 158 and fed to the signal means 146.

ALTERNATIVE EMBODIMENTS It will be understood by those skilled in the art that alternatively as shown in FIG. 1, the signal means 146 may comprise an audible signal means, such as a horn 100a of the Industrial Resonating type No. 54 20 manufactured by Graybar Electric Co., Inc., New York, New York, or a recording means, such as the strip chart recorder 16% of the single channel rectilinear type A601R manufactured by Esterline Angus Co., Inc., Indianapolis, Indiana, or the like.

Further, a line L, (FIG. 1) may connect the amplifier 158 to a solenoid valve 162 (FIG. 1) such as the NG467 type manufactured by Detroit Coil Co., Ferndale, Michigan, which valve 162 is mounted by means of a bracket 164 (FIG. 1) on the arm 108 of the frame 100. The valve 162 is disposed between a tube 166 (FIG. 1) (extending between a paint tank 168 (FIG. 1) and the solenoid valve 162) and is spray nozzle 170 (FIG. 1). When the solenoid valve l62'is energized, and opened by the amplified current signal from the amplifier 158, paint or the like is deposited at P (FIG. I) a predetermined distance D from the detecting point P (FIG. 1

For the purpose of removing any magnetic particles 54 which may collect on the detecting head 104, a suction device 172 (FIG. 1) is mounted by means of a bracket 174 (FIG. 1) on the arm 108 of the frame 100, has its suction tube 176 (FIG. 1) disposed adjacent the rotating detecting head I02 and is connected to a source of vacuum indicated in FIG. 1 by the legend to exhaust apparatus.

Referring now to FIG. 8, it will be understood that the detecting head 102 may be adapted to detect a defect 10 in a flat workpiece, such as a bar or plate 12 or the like. Current flow for the defect signal is indicated in FIG. 8 by the arrow dash lines. Further, the magnetic means may be a magnet energizing circuit where current flow is indicated by arrow dash-dot lines (FIG. 8) and has an electromagnet coil 136 (FIG. 8) which contacts connectors 178. The connector 178 is insulated from the detecting head I02 and the shaft 104 by insulating bushings 180,180a of nylon or the like. Each connector 178 is connected to a conducting ring 182 (FIG. 8) which, in turn, is connected by a contact brush assembly 184 through lines L9,L10 to a suitable supply of DC voltage indicated by the legend DC supply". The contact disk 140, in this case, is slidable laterally by means of the clearance aperture 142, engages the top 186 (FIG. 8) of the bar or plate 12 and is, of course, held to the detecting head 102' by means of magnetic attraction. The current passes through shaft 104",

ring 187 and line L8 to the south pole of the detecting head 102 As shown in FIGS. 9, 10, the apparatus 14 may be mounted on a carriage 188, which carriage 188 rides by means of wheels 190 on tracks 192. In this case, the drive means may comprise a motor 194 (FIG. 9) connected by means of a gear reduction unit 196 (FIG. 9) to the shaft 198 (FIG. 9) on which, for example, the rearward wheels 190 are mounted.

In FIG. 11, the signal from defect detecting drum 102 is carried by line L6 to a relay 200 of the sensitive solid state metering type, Model 12 or the like, made by Sensitak Instrument Corporation, Manchester, New Hampshire. The relay 200 is energizable by a transformer 202 such as a type 32-P-6l38 transformer made by Stancor Electronics, Inc., Chicago, Illinois.

The relay 200 energizes another relay 204,, a type 89-415XBX relay made by Struthers-Dunn, lnc., Pitman, New Jersey, which relay 200 closes normally open contacts 206, 208, 210 to energize respectively recorder 160b, light 160, horn 100a, or valve 162.

FIGS. 12, 13 show dual detection devices 98, each having a detection head 102 and a contact wheel 140 (shown in the right hand portions of FIG. 12 and similar in shape to the detector head 102 shown in FIG. 13) provided with either a permanent type magnet (not shown but similar to magnet 136 FIG. 6) or an electromagnet 203. Insulation bushing 138 is similar to insulation bushing 138 shown in FIG. 6. The detection devices 100 provide complete peripheral detection for the workpiece, such as a pipe 12 or the like. The dual detection devices 98 are supported so that the detection heads 102 are spaced from the pipe 12 and the contact wheels 140 are in engagement with the pipe 12.

FIG. 14 shows one detection device 98 of the type shown in FIGS. 12, 13 having a concave roll type or spool type cross roll type detection head 102 and a concave roll type or spool type cross roll type contact roll 140" to accommodate a wide range of sizes of the workpiece 12. The detection head 102 and contact roll 140 are diagonally disposed with respect to the workpiece or pipe 12. The detection device 98 is supported so that the detection head 102 is spaced from the workpiece l2 and the contact roll 140 is in engagement with the workpiece 12.

SUMMARY OF THE ACHIEVEMENTS OF THE OBJECTS OF THE INVENTION Itwill be recognized by those skilled in the art that the .objects of this invention have been achieved by providing an automatic magnetic particle inspection apparatus 14 (FIGS. 1-7) and 14 (FIGS. 9, which apparatus are rugged in construction, thereby enabling the apparatus 14 (FIGS. 1-7) and 14 (FIGS. 9, 10) to withstand severe mill or plant operating conditions; require little or no maintenance; operate on a magnetic bridging or switching principle thereby permitting the use of semi-skilled or unskilled operators; have a low installation cost; utilize a non-contact sensing feature in the form of a magnetic switch bridge which eliminates wear on the apparatus 14 (FIGS. I-7) and 14 (FIG. 9); provide a maximum utilization of magnetic powerthrough positive contact of one pole (i.e., the north pole N of the detecting heads 102 (FIGS. 1-7) and 102 (FIG. 8)) with the workpiece, either a pipe 12 (FIGS. 1-7) or a bar or plate 12 (FIG. 8); and provides a simple method of automating such apparatus.

While in accordance with the patent statutes, preferred and alternative embodiments of this invention have been illustrated and described in detail, it is to be particularly understood that the invention is not limited thereto or thereby.

I claim:

1. An automatic magnetic particle inspection system for detecting a defect in a workpiece and for signalling the presence of said defect in said workpiece, said system having:

a. conveying means for supporting said workpiece and a magnetic particle inspection apparatus;

b. drive means connected to one of said conveying means and said apparatus for causing relative movement between said workpiece and said apparatus to convey either said workpiece or said apparatus along a path of movement, said apparatus having:

c. magnetizing means disposed adjacent said path of movement of said workpiece and for creating lines of flux in said workpiece and fringe lines of flux adjacent said defeet in an attraction zone;

. magnetic particle spray means disposed further along said path of movement of said workpiece for spraying magnetic particles on said magnetized workpiece to deposit said magnetic particles on said workpiece in a spray zone adjacent said attraction zone and to create a pile of said magnetic particles adjacent said defect in said attraction zone within said spray zone;

e. detecting and signalling means disposed further along said path of movement of said workpiece and having: 1 a bi-pole detecting head,

a. said detecting head being spaced from said attraction zone a predetermined distance and having: I. magnet means and a contact member for contacting said workpiece,

a. said magnet means being operable to create lines of flux through one pole of said detecting head, said contact member, said workpiece, said pile of magnetic particles, said other pole of said detecting head to said magnetic means to form said pile of magnetic particles into a bridge across said predetermined distance,

2. signal means for indicating the presence of said defect,

and

3. control mean connected to said detecting head and said signal means and energized by said bridge to actuate said signal means to indicate the presence of said defect.

2. For an automatic magnetic particle inspection system for detecting a defect in a workpiece and for signalling the presence of said defect in said workpiece, said system having conveying means for supporting said workpiece and a mag netic particle inspection apparatus, drive means connected to one of said conveying means and said apparatus for causing relative movement between said workpiece and said apparatus to convey either said workpiece or said apparatus along a path of movement, said apparatus having magnetizing means disposed adjacent said path of movement of said workpiece and for creating lines of flux in said workpiece and fringe lines of flux adjacent said defect in an attraction zone, magnetic particle spray means disposed further along said path of movement of said workpiece for spraying magnetic particles on said magnetized workpiece to deposit said magnetic particles on said workpiece in a spray zone adjacent said attraction zone and to create a pile of said magnetic particles adjacent said defect in said attraction zone within said spraying zone:

a. detecting and signalling means disposed further along said path of movement of said workpiece and having: 1. a bi-pole detecting head,

a. said detecting head being spaced from said attraction zone a predetermined distance and having: 1. magnetic means and a contact member for contacting said workpiece,

a. said magnetic means being operable to create lins of flux through one pole of said detecting head, said contact member, said workpiece, said pile of magnetic particles, said other pole of said detecting head to said magnetic means to form said pile of magnetic particles into a bridge across said predetermined distance,

2. signalling means for indicating the presence of said defeet, and

3. control means connected to said detecting head and said signal means and energized by said bridge to activate said signal means to indicate the presence of said defect.

3. The apparatus recited in claim 1 wherein said signal means is a marking means disposed along the path of movement and operable to mark the workpiece a fixed distance from said detector head.

4. The apparatus recited in claim 1 wherein said signal means is a visible means.

5. The apparatus recited in claim 1 wherein said signal means is an audible means.

7. The apparatus recited in claim 1 wherein said signal means is a recording means.

7. The apparatus recited in claim 1 and having magnetic particle collecting means disposed along said path of movement to collect said magnetic particles in said spray zone outside said attraction zone.

8. The apparatus recited in claim 1 wherein said detecting and signalling means has suction means adjacent said detecting head for collecting magnetic particles from said detecting head. i

9. The apparatus recited in claim 1 wherein said detecting head is rotatable.

10. The apparatus recited in claim 9 and having head drive means connected to said detecting head to rotate said detecting head.

11. The apparatus recited in claim 10 and having tensioning means associated with said head drive means to insure positive rotation of said detecting head.

12. The apparatus recited in claim 10 wherein said drive means is in engagement with said workpiece and is driven by said workpiece.

13. The apparatus recited in claim 1 and having contact assembly disposed between said detecting head and said control means.

14. The apparatus recited in claim 1 wherein said detecting head spans the periphery of the workpiece and has a peripheral cavity spaced said predetermined distance from said attraction zone.

15. The apparatus recited in claim 1 wherein said control means has'a contact brush in engagement with said detecting head.

16. The apparatus recited in claim 1 wherein said contact member is a disk.

17. The apparatus recited in claim 1 wherein said contact member spans the periphery of the workpiece.

18. The apparatus recited in claim 1 wherein said contact member is a concave roll.

19. The apparatus recited in claim 1 wherein said detecting head is a concave roll.

i i i i t 

1. An automatic magnetic particle inspection system for detecting a defect in a workpiece and for signalling the presence of said defect in said workpiece, said system having: a. conveying means for supporting said workpiece and a magnetic particle inspection apparatus; b. drive means connected to one of said conveying means and said apparatus for causing relative movement between said workpiece and said apparatus to convey either said workpiece or said apparatus along a path of movement, said apparatus having: c. magnetizing means disposed adjacent said path of movement of said workpiece and for creating lines of flux in said workpiece and fringe lines of flux adjacent said defect in an attraction zone; d. magnetic particle spray means disposed further along said path of movement of said workpiece for spraying magnetic particles on said magnetized workpiece to deposit said magnetic particles on said workpiece in a spray zone adjacent said attraction zone and to create a pile of said magnetic particles adjacent said defect in said attraction zone within said spray zone; e. detecting and signalling means disposed further along said path of movement of said workpiece and having:
 1. a bi-pole detecting head, a. said detecting head being spaced from said attraction zone a predetermined distance and having:
 1. magnet means and a contact member for contacting said workpiece, a. said magnet means being operable to create lines of flux through one pole of said detecting head, said contact member, said workpiece, said pile of magnetic particles, said other pole of said detecting hEad to said magnetic means to form said pile of magnetic particles into a bridge across said predetermined distance,
 2. signal means for indicating the presence of said defect, and
 3. control mean connected to said detecting head and said signal means and energized by said bridge to actuate said signal means to indicate the presence of said defect.
 2. signal means for indicating the presence of said defect, and
 2. For an automatic magnetic particle inspection system for detecting a defect in a workpiece and for signalling the presence of said defect in said workpiece, said system having conveying means for supporting said workpiece and a magnetic particle inspection apparatus, drive means connected to one of said conveying means and said apparatus for causing relative movement between said workpiece and said apparatus to convey either said workpiece or said apparatus along a path of movement, said apparatus having magnetizing means disposed adjacent said path of movement of said workpiece and for creating lines of flux in said workpiece and fringe lines of flux adjacent said defect in an attraction zone, magnetic particle spray means disposed further along said path of movement of said workpiece for spraying magnetic particles on said magnetized workpiece to deposit said magnetic particles on said workpiece in a spray zone adjacent said attraction zone and to create a pile of said magnetic particles adjacent said defect in said attraction zone within said spraying zone: a. detecting and signalling means disposed further along said path of movement of said workpiece and having:
 2. signalling means for indicating the presence of said defect, and
 3. control means connected to said detecting head and said signal means and energized by said bridge to activate said signal means to indicate the presence of said defect.
 3. The apparatus recited in claim 1 wherein said signal means is a marking means disposed along the path of movement and operable to mark the workpiece a fixed distance from said detector head.
 3. control mean connected to said detecting head and said signal means and energized by said bridge to actuate said signal means to indicate the presence of said defect.
 4. The apparatus recited in claim 1 wherein said signal means is a visible means.
 5. The apparatus recited in claim 1 wherein said signal means is an audible means.
 7. The apparatus recited in claim 1 wherein said signal means is a recording means.
 7. The apparatus recited in claim 1 and having magnetic particle collecting means disposed along said path of movement to collect said magnetic particles in said spray zone outside said attraction zone.
 8. The apparatus recited in claim 1 wherein said detecting and signalling means has suction means adjacent said detecting head for collecting magnetic particles from said detecting head.
 9. The apparatus recited in claim 1 wherein said detecting head is rotatable.
 10. The apparatus recited in claim 9 and having head drive means connected to said detecting head to rotate said detecting head.
 11. The apparatus recited in claim 10 and having tensioning means associated with said head drive means to insure positive rotation of said detecting head.
 12. The apparatus recited in claim 10 wherein said drive means is in engagement with said workpiece and is driven by said workpiece.
 13. The apparatus recited in claim 1 and having contact assembly disposed between said detecting head and said control means.
 14. The apparatus recited in claim 1 wherein said detecting head spans the periphery of the workpiece and has a peripheral cavity spaced said predetermined distance from said attraction zonE.
 15. The apparatus recited in claim 1 wherein said control means has a contact brush in engagement with said detecting head.
 16. The apparatus recited in claim 1 wherein said contact member is a disk.
 17. The apparatus recited in claim 1 wherein said contact member spans the periphery of the workpiece.
 18. The apparatus recited in claim 1 wherein said contact member is a concave roll.
 19. The apparatus recited in claim 1 wherein said detecting head is a concave roll. 